Conventionally, wiring is formed on fine grooves for wiring, holes, or resist openings provided on a surface of a substrate such as a semiconductor wafer, and bumps (protruding electrode) electrically connected to electrodes of a package or similar component is formed on the surface of the substrate. As such method for forming these wiring and bump, a method such as an electrolytic plating method, a deposition method, a printing method, and a ball bump method has been known. In accordance with recent increase in the number of I/Os of a semiconductor chip and recent decrease in pitch, the electrolytic plating method that allows miniaturization and provides comparatively stable performance has been often used.
In an apparatus performing the electrolytic plating, an anode and a substrate are generally disposed so as to be mutually opposed in a plating bath that houses plating solution, and a voltage is applied to the anode and the substrate. This forms a plating film on the substrate surface.
When the plating film is formed by the electrolytic plating method, various kinds of additives are generally mixed with the plating solution. Mixing the additive with the plating solution allows obtaining, for example, an effect of promoting or reducing the film formation speed of the plating film and an effect of improving the film quality of the plating film.
As the anode used by the electrolytic plating apparatus, there has been conventionally used a soluble anode that dissolves in plating solution and an insoluble anode that does not dissolve in the plating solution. Usually, when the plating film is formed on the substrate, the additive is adsorbed into and consumed by the plating film. In addition, performing a plating process using the insoluble anode generates oxygen by a reaction of the insoluble anode with the plating solution and the additive reacts with this oxygen to be decomposed. Additionally, the additive is also decomposed through a contact with the insoluble anode. The decomposition of the additive causes the additive to lose the above-described effects, causing a problem that the desired film cannot be obtained on the substrate surface. To prevent this problem, it is only necessary to add the additive to the plating solution as needed such that the concentration of the additive in the plating solution is maintained at a certain level or more. However, since the additive is expensive, the decomposition of the additive is desirably reduced as much as possible.